The present invention relates to photographic cameras which include, as an integral part, a flash unit for momentarily illuminating objects to be photographed. More particularly, the invention relates to a camera in which light from an integral flash unit is directed into object space through the camera's viewfinder.
Generally speaking, electronic flash units of the type used with photographic still cameras are either of an accessory nature, being detachably coupled to the top or the side of the camera housing, or of an integral nature, being built-in to the camera housing. Examples of cameras having accessory and integral flash units are respectively disclosed in U.S. Pat. No. 3,437,021 and 3,357,328.
While cameras having integral flash units are usually less bulky and, hence, less cumbersome to use and carry than cameras requiring accessory-type flash units, they are nevertheless considerably bulkier than cameras having no flash capability. The reason for this increased bulk is that it has been common heretofore to position the unit's flashlamp and its associated optical elements on the front surface of the camera housing. Since these elements consume space, the camera housing must be of a size to accommodate them. Added to the disadvantage of the increased bulk, the placement of a flash unit on the front surface of the camera housing often detracts from the aesthetic appearance of the camera. In these days of ever-increasing interest in minimizing camera bulk and streamlining camera design, it would be desirable for a camera having an integral flash unit to be no bulkier than and be as streamlined as a camera without flash capability.
To satisfy the above desire, some cameras embodying integral flash units store the flash unit out of sight within the camera housing. For example, in U.S. Pat. No. 4,153,355 issued on May 8, 1979, a camera is disclosed having an integral flash unit which is slidably mounted on the camera housing for movement between a retracted position with the camera housing and a pop-up position outside the housing. In its retracted position, the flashlamp is inoperable and hidden from sight; in its pop-up position, the flashlamp is in an exposed position to illuminate the scene. When not being used, cameras of this type are only slightly bulkier than similar cameras having no flash capability; in use, however, the flashlamp is located where it can be mishandled and damaged, or worse yet, can cause injury to the camera user.
In addition to the aforementioned disadvantages, cameras embodying integral flash units are particularly subject to the so-called "finger-over flash" failure. As cameras become increasingly smaller in size, proper handling of the camera at the time of exposure becomes more critical. Human factors engineers report that a substantial percentage of underexposed photographs is caused by an obstruction in the optical path of the flashlamp. Typically, this obstruction is the photographer's finger which, during the picture composing period, becomes inadvertently moved to an obstructing position. It would be desirable, therefore, for a camera user to be able to detect such an obstruction prior to shutter actuation so that he can take corrective measures.